This invention relates to a hard laminated film whereof the crystal particle size is finely controlled having superior mechanical resistance, to a hard laminated film having wear resistance formed on the surface of machining tools or sliding parts for automobiles, and to a hard laminated film having superior wear resistance and anti-oxidation properties.
This invention further relates to a composite film-forming device comprising an arc vaporization source and a sputter vaporization source which can form this hard laminated film having superior properties.
In recent years, there has been an increasing need to improve the wear resistance of super hard alloys, cutting tools having thermit or high-speed tool steel as base materials and sliding parts for automobiles, and the possibility of improving the wear resistant film used on the surface of these parts is being considered.
The wear resistant film used in the prior art comprises a hard film such as TiAlN, which is a composite nitride film of TiN or TiCN, Ti and Al, coated on this base material (part).
To attempt to improve the wear resistance of this wear-resistant film, a third element was generally added in order to increase the fineness of the crystal particles of the film and improve its properties. For example, in the case of cutting tools, it has been reported that the addition of Si or B to a TiAlN film improves wear resistance and increases hardness by increasing the fineness of crystal particles (U.S. Pat. No. 5,580,653 and U.S. Pat. No. 5,318,840). Also, it has been proposed to add B to the CrN film used in sliding parts such as the piston ring of an automobile to improve wear resistance by increasing hardness (U.S. Pat. No. 6,232,003).
Regarding addition of elements to hard films in the prior art, there is also an example of an attempt to improve properties such as hardness by adding Si by sputtering while forming a TiN film by an arc vaporization source in a device provided with both an arc and sputter vaporization source so as to form a TiSiN film (K. H. Kim et al, Surf. Coat. Technol. 298(2002) pp. 243-244, 247).
In these methods for increasing the fineness of crystal particles of a wear-resistant film by adding other elements, the fineness of the crystal particles is determined by the addition amount of the element, and the film particle size can be controlled only by varying the addition amount of the element. Therefore, to manufacture films having different particle sizes, plural targets having varying element addition amounts must be produced. However, it is extremely difficult to manufacture a sample having exactly the right particle size for a particular purpose, i.e., to manufacture a film having properties designed for a particular purpose, and there are practical problems involved.
Hard films with superior hardness and wear resistance having an essentially rock-salt crystal structure have also been proposed for use in cutting tools (U.S. Pat. No. 6,767,658, U.S. Patent No. 2002-168552). These hard film compositions are, for example, (Tia, Alb, Vc)(C1−dNd), wherein,0.02≦a≦0.3, 0.5≦b≦0.8, 0.05<c, 0.7≦b+c, a+b+c=1, 0.5≦d≦1
(a, b, c are respectively the atomic ratios of Ti, Al, V, and d is the atomic ratio of N).
In general, hard films having a rock-salt structure can be measured by X-ray diffraction by the θ-2θ method. For example, hard films such as ((TiAlV)(CN) have a rock-salt crystal structure, and form a composite nitride having a rock-salt structure in which Al and V replace the Ti and TiN sites in the rock-salt. In this case, the AlN in the rock-salt structure (grating constant 4.12 Å) is a high temperature, high pressure phase and a very hard substance, and if the ratio of Al in (CN)(TiAlV) is increased while maintaining the rock-salt structure, the hardness of the (TiAlV)(CN) film can be further increased.
To form a multi-layer hard film of this type, there are an devices and methods which can combine plural arc vaporization sources and sputter vaporization sources or electron beam vaporization sources to form different hard film layers on a substrate depending on the hard materials used.
Among these, a device which combines plural arc vaporization sources and sputter vaporization sources to sequentially form hard film layers on the substrate is said to have a high film-forming efficiency from the viewpoint that the film can be formed by making use of the different properties of an arc vaporization source and sputter vaporization source.
For example, concerning the relative properties of an arc vaporization source and a sputter vaporization source, the arc vaporization source forms a film more rapidly than a sputter vaporization source, but it is difficult to adjust the film-forming rate, and difficult to precisely control the thickness of the thin film layer which is formed. On the other hand, the sputter vaporization source forms a film more slowly than an arc vaporization source, but the film-forming rate can be easily adjusted, and as it can be operated even with a very extremely small input power, the thickness of the thin film which is formed can be precisely controlled.
Consequently, by using an arc vaporization source for relatively thick film layers and a sputter vaporization source for relatively thin film layers, the thickness of each film layer can be easily controlled, and the overall film-forming rate can be accelerated.
A composite film-forming device is known in the art wherein plural arc vaporization sources and sputter vaporization sources are combined in the same film-forming chamber.
For example, a method to form a hard film has been proposed wherein the arc vaporization source and sputter vaporization source are operated alternately. First, metal ion etching is performed by the arc vaporization source, then the arc vaporization source is stopped, a process gas is introduced, and the sputter vaporization source is operated (U.S. Pat. No. 5,234,561).
A device has also been proposed which combines a magnetic field applying mechanism with an arc vaporization source and sputter vaporization source (European Patent No. 0403552, U.S. Pat. No. 6,232,003). In FIG. 7 of U.S. Pat. No. 6,232,003, one of the prior art techniques which does not have a magnetic field applying mechanism, the magnetic fields of the arc vaporization source and sputter vaporization source mutually interfere with each other.
It is also known in the art that the arc vaporization source and sputter vaporization source can be operated simultaneously to form a hard film, and when a third element is added to the film, the fineness of the crystal particles of the film increases which improves wear resistance and other properties. For example, a method has been proposed wherein Si or B is added to a TiN film or a TiAlN film for cutting tools which improves wear resistance, and increases hardness due to the finer crystal particles (U.S. Pat. Nos. 5,580,653, 5,318,840, K. H. Kim et al, Surf. Coat. Technol. 298(2002) pp. 243-244, 247). A method has also been proposed wherein B is added to a CrN film used in sliding parts such as the piston ring of automobiles to improve wear resistance by increasing hardness (U.S. Pat. No. 6,232,003).
Even in a hard film having mainly a halide crystal structure, depending on the film-forming conditions, if the crystal particle size (hereafter, referred to also as crystal size) of the halide hard film is coarse, there is a limit to the improvement of wear resistance which can be obtained by increased hardness.
In the aforesaid prior art, a specific element was uniformly added during film-forming in every case, and a single layer film having a single chemical composition was thereby formed. The film formed in this way does have increased hardness and improved wear resistance due to the finer crystal particles forming the film, but if the frictional coefficient of the film surface was not sufficiently reduced, there was little improvement of wear resistance and lubricity, and due to the increased hardness, the film was more liable to damage other members, hence, further improvement was desired.
Moreover, hard films formed by these prior art methods and techniques did not have sufficient performance to satisfy the increasingly stringent demands of cutting tools and sliding parts, so enhanced wear resistance and better durability were required.
For example, if an element such as B or Si is added to the aforesaid wear-resistant film so as to increase the fineness of the crystal particles, the fineness is determined by the element addition amount, and the film particle size can be controlled only by varying the addition amount. Therefore, to manufacture films of different particle sizes, plural targets with varying element addition amounts must be prepared. It is thus very inconvenient to produce a sample having a specific particle size for a particular purpose, i.e., a film having properties designed for a particular purpose, and there is therefore a practical limit to the wear resistance enhancement of the hard film which can be obtained.
In the case of the aforesaid device, if an arc vaporization source and sputter vaporization source were operated in the same film-forming chamber, even if the arc vaporization source and sputter vaporization source were operated alternately, various problems could not be avoided, e.g., it was sometimes difficult to form a fine hard film or hard film having the desired composition depending on the hard film material and film-forming conditions, and abnormal electrical discharges sometimes occurred during the film-forming process. Consequently, there was also a limit to the wear resistance enhancement which could be obtained by increasing the hardness of the film.
For example, when forming hard nitride films such as TiN, TiCN or TiAlN, film-forming is performed in a mixed gas atmosphere of Ar and nitrogen to form the nitride. However, in the same film-forming chamber, electrons discharged from the arc vaporization source or sputter vaporization source tend to be easily attracted to the chamber walls which act as an anode in the same way as the substrate. As a result, the concentration of discharged electrons becomes sparser, collisions with the sputter gas or reactive gas decrease, and it is difficult to perform high efficiency gas ionization.
Further, in a sputter vaporization source, an inert sputter gas such as Ar (argon), Ne (neon) or Xe (xenon) is used whereas in an arc vaporization source, a reactive gas (reaction gas) such as nitrogen, methane or acetylene is used. Consequently, if arc film-forming and sputter film-forming are simultaneously performed in the same film-forming chamber, and particularly when the partial pressure of the reactive gas such as nitrogen is increased in order to improve film-forming performance, the sputter target material may react with the reaction gas depending on the sputter vaporization source material used so as to produce an insulator (insulating substance) on the target material surface. Due to this insulator, there is a high probability of an abnormal discharge (arcing) occurring in the sputter vaporization source. This also interferes with high efficiency gas ionization.
If there is interference with high efficiency gas ionization, ionic irradiation to the substrate cannot be intensified, so the fineness of the hard film layer cannot be increased, the surface becomes coarser and surface properties decline. As a result, in the prior art film-forming device, and particularly when an arc vaporization source and sputter vaporization source were operated simultaneously in the same film-forming chamber, there was a serious limitation to the enhancement of properties and performance which can be achieved by increasing film hardness.
It is therefore an object of this invention, which was conceived in view of the above problems, to provide a hard film with improved properties such as wear resistance, a hard film having superior wear resistance and lubricity to those of prior art hard films, and a hard laminated film with superior wear resistance and anti-oxidation properties by increasing the fineness of the crystal particles of a rock-salt hard film. Further, it is an object of this invention to provide a composite film-forming device and sputter vaporization source which permits a hard film having desired properties to be obtained without any problems in the film-forming process when an arc vaporization source and sputter vaporization source are operated simultaneously in the same film-forming chamber.